Pneumatic Tire

ABSTRACT

A pneumatic tire includes first main grooves formed on outer sides, in the lateral direction, of a first land including an equatorial plane and extending in the circumferential direction; second main grooves outside, in the lateral direction, of the first main grooves and extending in the circumferential direction; auxiliary grooves formed on second lands between the first main grooves and the second main grooves, opening to the second main grooves, and terminating in the second lands; and first sipes inclined identically to the auxiliary grooves and crossing the second lands. The auxiliary grooves are formed into a shape bending at a bend point, and include a first portion extending from an opening end to the bend point, and a second portion extending from the bend point to a terminating end. A groove width of the first portion gradually reduces from the opening end to the bend point.

PRIORITY CLAIM

Priority is claimed to Japan Patent Application Serial No. 2017-105904filed on May 29, 2017.

TECHNICAL FIELD

The present technology relates to a pneumatic tire.

BACKGROUND ART

Pneumatic tires including all-season tires may be required to have atread pattern capable of increasing a tire's residual cornering force(hereinafter referred to as residual CF) for controlling drifting of avehicle to ensure straight-line performance. Snow performancerepresenting running performance on snow is important for all-seasontires. However, when the snow performance is improved, quietness mightlower depending on a tread pattern. Such a pneumatic tire is known thatimproves both snow performance and quietness (e.g., Japan UnexaminedPatent Publication No. 2014-205410). The pneumatic tire described inJapan Unexamined Patent Publication No. 2014-205410 can be furtherenhanced in improving snow performance, quietness, and residual CF.

SUMMARY

The present technology provides a pneumatic tire capable of improvingsnow performance, quietness, and residual CF.

A pneumatic tire according to the technology includes: a pair of firstmain grooves that are formed on both outer sides, in a tire lateraldirection, of a first land portion including a tire equatorial plane,and that each extend in a tire circumferential direction; a pair ofsecond main grooves that lie outside, in the tire lateral direction, ofthe first main grooves, and that each extend in the tire circumferentialdirection; auxiliary grooves that are formed on each of second landportions between each of the first main grooves and each of the secondmain grooves, that each open to each of the second main grooves, andthat each terminate in each of the second land portions; and first sipesthat are inclined in a direction identical to a direction of theauxiliary grooves, and that cross each of the second land portions. Theauxiliary grooves are each formed into a shape bending at a bend point,and each include a first groove portion extending from an opening endportion at which each of the auxiliary grooves opens to the bend point,and a second groove portion extending from the bend point to aterminating end portion at which each of the auxiliary groovesterminates. A groove width of each of the first groove portionsgradually reduces from the opening end portion to the bend point.

It is preferable that the pair of first main grooves and the pair ofsecond main grooves be each formed into a zigzag shape having groovewalls having short portions and long portions, when viewed in a plan,and an inclination direction of the zigzag shapes be identical to thedirection of the auxiliary grooves.

It is preferable that the second main grooves define third land portionsoutside, in the tire lateral direction, of the second main grooves, andlug grooves that are not communicated with the second main grooves befurther provided on the third land portions.

It is preferable that circumferential narrow grooves each of which isformed into a zigzag shape inclined in a direction of the auxiliarygrooves, and extends in the tire circumferential direction be furtherprovided on the third land portions.

It is preferable that the lug grooves be inclined, in regions X rangingfrom 90% or more to 110% or less of a ground contact width centeredaround the tire equatorial plane, at an angle α in a range of +/−10degrees or less. The angle α may be formed with a straight line alongthe tire lateral direction and a straight line joining midpoints, atboth end portions of each of the regions X, of a groove width of each ofthe lug grooves. In regions each lying closer to the tire equatorialplane than the regions X, the lug grooves may be inclined in a directionidentical to the inclination direction of the auxiliary grooves.

It is preferable that, in the regions each lying closer to the tireequatorial plane than the regions X ranging from 90% or more to 110% orless of the ground contact width centered around the tire equatorialplane, three-dimensional (3D) sipes inclined in a direction identical tothe inclination direction of the lug grooves be further included.

It is preferable that a distance between a boundary portion between eachof the short portions and each of the long portions of the groove wallsof the second main grooves and an end portion, lying adjacent to thetire equatorial plane, of each of the lug grooves range from 1.0 timesor more to 4.0 times or less of a length of each of the short portionsin the tire circumferential direction. It is also preferable that theboundary portion lie within a range of +/−5 degrees of a direction fromone of the midpoints of the groove width of each of the lug grooves, atthe end portion of each of the regions X ranging from 90% or more to110% or less of the ground contact width centered around the tireequatorial plane, the end portion lying adjacent to the tire equatorialplane, to the end portion, lying adjacent to the tire equatorial plane,of each of the lug grooves.

It is preferable that, in each of the first groove portions, a groovedepth gradually increase from the bend point to the opening end portion.

It is preferable that, in each of the first groove portions, the groovewidth at the bend point range from 50% or more to 90% or less of thegroove width at the opening end portion.

It is preferable that, in each of the first groove portions, the groovedepth at the opening end portion range from 110% or more to 150% or lessof the groove depth at the bend point.

It is preferable that the first main grooves be each disposed outside,in the tire lateral direction, of the tire equatorial plane. The firstmain grooves may define the first land portion. First land portion sipesmay be further included. The first land portion sipes may open to eachof the first main grooves. The first land portion sipes may eachterminate in the first land portion.

It is preferable that the auxiliary grooves be inclined in the tirelateral direction so that a straight line joining each of the openingend portions and each of the terminating end portions approaches thetire equatorial plane relative to the tire circumferential direction.

It is preferable that the pair of first main grooves be each formed intothe zigzag shape having the groove walls having the short portions andthe long portions, when viewed in a plan. The zigzag shapes may each beformed with the long portions and the short portions alternately andrepeatedly disposed in the tire circumferential direction. A length ofeach of the long portions in the tire circumferential direction mayrange from 10 times or more to 25 times or less of a length of each ofthe short portions in the tire circumferential direction.

It is preferable that the pair of first main grooves be each formed withthe groove wall lying outside in the tire lateral direction and thegroove wall lying inside in the tire lateral direction and adjacent tothe tire equatorial plane. The long portions and the short portions maybe disposed at identical pitches. Arrangement phases of the longportions and the short portions may differ between each of the groovewalls lying outside in the tire lateral direction and each of the groovewalls lying inside in the tire lateral direction and adjacent to thetire equatorial plane.

It is preferable that the pair of second main grooves be each formedinto the zigzag shape having the groove walls having the short portionsand the long portions, when viewed in a plan. The zigzag shapes may eachbe formed with the long portions and the short portions alternately andrepeatedly disposed in the tire circumferential direction. A length ofeach of the long portions in the tire circumferential direction mayrange from 10 times or more to 25 times or less of a length of each ofthe short portions in the tire circumferential direction.

It is preferable that the pair of second main grooves be each formedwith the groove wall lying outside in the tire lateral direction and thegroove wall lying inside in the tire lateral direction and adjacent tothe tire equatorial plane. The long portions and the short portions maybe disposed at identical pitches. Arrangement phases of the longportions and the short portions may differ between each of the groovewalls lying outside in the tire lateral direction and each of the groovewalls lying inside in the tire lateral direction and adjacent to thetire equatorial plane.

It is preferable that an arrangement pitch in the tire circumferentialdirection of each of the long portions and each of the short portions oneach of the pair of second main grooves and an arrangement pitch in thetire circumferential direction of the lug grooves that are provided oneach of the third land portions respectively defined outside, in thetire lateral direction, of the second main grooves, and that are notrespectively communicated with the second main grooves be identical toeach other. It is also preferable that an end portion of each of the luggrooves be disposed to face each of the short portions on each of thegroove walls lying outside, in the tire lateral direction, of the secondmain grooves.

With the pneumatic tire according to the present technology, snowperformance, quietness, and residual CF can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a meridian cross-sectional view illustrating a pneumatic tireaccording to an embodiment of the present technology.

FIG. 2 is a developed view illustrating a tread pattern of the pneumatictire according to the embodiment of the present technology.

FIG. 3 is an enlarged plan view illustrating one of second land portionsand one of third land portions, for example, on one side of the treadpattern in FIG. 2.

FIG. 4 is an enlarged plan view illustrating the one of the second landportions on the tread pattern in FIG. 2.

FIG. 5 is a partial-cut perspective view illustrating the one of thesecond land portions on a tread portion in FIG. 3.

FIG. 6 is a cross-sectional view of the one of the second land portions,taken along a center of a groove width of one of first groove portionson the tread portion in FIG. 3.

FIG. 7 is a cross-sectional view of the one of the second land portions,taken along a center of a groove width of one of second groove portionson the tread portion in FIG. 3.

FIG. 8 is a view illustrating an example of a ground contact shape withrespect to the tread pattern in FIG. 2.

FIG. 9 is a partial enlarged view of the one of the third land portionsin FIG. 8.

DETAILED DESCRIPTION

A pneumatic tire according to an embodiment of the present technologywill now be described herein in detail with reference to the drawings.However, the technology is not limited to the embodiment. Moreover,constituents of the embodiment include elements that are substitutablewhile maintaining consistency with the technology, and obviouslysubstitutable elements. Furthermore, the modified examples described inthe embodiment can be combined as desired within the scope apparent tothose skilled in the art.

FIG. 1 is a meridian cross-sectional view illustrating a pneumatic tireaccording to an embodiment of the present technology. FIG. 2 is adeveloped view illustrating a tread pattern of the pneumatic tireaccording to the embodiment of the present technology. FIG. 3 is anenlarged plan view illustrating one of second land portions and one ofthird land portions, for example, on one side of the tread pattern inFIG. 2. FIG. 4 is an enlarged plan view illustrating the one of thesecond land portions on the tread pattern in FIG. 2.

Herein, “tire radial direction” refers to the direction orthogonal tothe rotation axis (not shown) of a pneumatic tire 10. “Inward in thetire radial direction” refers to the direction toward the rotation axisin the tire radial direction. “Outward in the tire radial direction”refers to the direction away from the axis of rotation in the tireradial direction. “Tire circumferential direction” refers to thecircumferential direction about the rotation axis regarded as the centeraxis. In addition, “tire lateral direction” refers to the directionparallel to the above described tire rotation axis. “Inward in the tirelateral direction” refers to the direction toward a tire equatorialplane CL in the tire lateral direction. “Outward in the tire lateraldirection” refers to the direction away from the tire equatorial planeCL in the tire lateral direction. “Tire equatorial plane CL” refers tothe plane that is orthogonal to the rotation axis of the pneumatic tire10 and that passes through the center of the tire width of the pneumatictire 10. “Tire width” refers to the width in the tire lateral directionbetween components located outward in the tire lateral direction, or, inother words, the distance between the components that are the mostdistant from the tire equatorial plane CL in the tire lateral direction.“Tire equator line” refers to the line that extends in the tirecircumferential direction of the pneumatic tire 10 and that lies on thetire circumferential equatorial plane CL. In the present embodiment, thetire equator line and the tire equatorial plane are denoted by the samereference sign CL.

As illustrated in FIG. 1, the pneumatic tire 10 according to the presentembodiment includes an annular tread portion 1 extending in the tirecircumferential direction, a pair of sidewall portions 2 and 2 disposedon both sides of the tread portion 1, and a pair of bead portions 3 and3 disposed inward of the sidewall portions 2 and 2 in the tire radialdirection.

A carcass layer 4 is mounted between the pair of bead portions 3 and 3.The carcass layer 4 includes a plurality of reinforcing cords extendingin the tire radial direction and is folded back around bead cores 5disposed in each of the bead portions 3 from a tire inner side to a tireouter side. A bead filler 6 having a triangular cross-sectional shapeand made of rubber composition is disposed on the outer circumference ofeach of the bead cores 5.

A plurality of belt layers 7 are embedded on an outer circumferentialside of the carcass layer 4 in the tread portion 1. The belt layers 7include a plurality of reinforcing cords that are inclined with respectto the tire circumferential direction, and the direction of thereinforcing cords of the different layers intersect with each other. Inthe belt layers 7, an inclination angle of the reinforcing cords withrespect to the tire circumferential direction ranges from, for example,10 degrees to 40 degrees. Steel cords are preferably used as thereinforcing cords of the belt layers 7. To improve high-speeddurability, at least one belt cover layer 8 formed by arrangingreinforcing cords at an angle of, for example, not greater than 5degrees with respect to the tire circumferential direction, is disposedon an outer circumferential side of the belt layers 7. Nylon, aramid, orsimilar organic fiber cords are preferably used as the reinforcing cordsof the belt cover layer 8.

Note that the tire internal structure described above represents atypical example for a pneumatic tire, and the pneumatic tire is notlimited thereto. Tread portion

FIG. 2 is a plan view illustrating a tread pattern of the pneumatic tire10 illustrated in FIG. 1. Note that the reference sign T denotes a tireground contact edge.

As illustrated in FIG. 2, the pneumatic tire 10 includes, on the treadportion 1, a pair of first main grooves 11 that lie on both outer sides,in the tire lateral direction, of the tire equatorial plane CL and thatextend in the tire circumferential direction, a pair of second maingrooves 12 that lie outside, in the tire lateral direction, of the firstmain grooves 11 and that extend in the tire circumferential direction,and auxiliary grooves 31 each formed on each of second land portions 22between each of the first main grooves 11 and 11 and each of the secondmain grooves 12 and 12.

As illustrated in FIG. 2, the tread portion 1 is formed with the pair offirst main grooves 11 that lie on both sides of the tire equatorialplane CL, and that extend in the tire circumferential direction, and thepair of second main grooves 12 that lie outside, in the tire lateraldirection, of the first main grooves 11, and that extend in the tirecircumferential direction. The first main grooves 11 and the second maingrooves 12 are circumferential grooves with wear indicators thatindicate the terminal stage of wear and that each typically has a groovewidth of 5.0 mm or greater and a groove depth of 7.5 mm or greater. Thegroove widths and the groove depths of the first main grooves 11 and thesecond main grooves 12 are not limited to the above described ranges.

Moreover, “lug groove”, described later, refers to a lateral groovehaving a groove width of 2.0 mm or greater and a groove depth of 3.0 mmor greater. Additionally, “sipe”, described later, refers to a cutformed on a land portion, which typically has a groove width of lessthan 1.5 mm.

The tread portion 1 formed with the first main grooves 11 and the secondmain grooves 12 is divided into a plurality of land portions.Specifically, when defined by the first main grooves 11, the treadportion 1 is formed with a land portion between the pair of first maingrooves 11, representing a first land portion 21 that intersects thetire equatorial plane CL, and that extends in the tire circumferentialdirection. When defined by the first main grooves 11 and the second maingrooves 12, the tread portion 1 is formed with land portions each layingbetween each of the first main grooves 11 and each of the second maingrooves 12, representing second land portions 22 that extend in the tirecircumferential direction. The tread portion 1 is further formed withland portions outside, in the tire lateral direction, of the second maingrooves 12, representing third land portions 23.

The second land portions 22 are provided on both sides of the tireequatorial plane CL. The second land portions 22 on both sides of thetire equatorial plane CL are shaped and rotated 180 degrees from eachother. The second land portions 22 are thus disposed in a point symmetrymanner around the tire equatorial plane CL.

Each of the second land portions 22 between each of the first maingrooves 11 and each of the second main grooves 12 is formed with aplurality of the auxiliary grooves 31 each separated at intervals in thetire circumferential direction. The auxiliary grooves 31 are each formedinto a bent shape, similar to a fishing hook. As illustrated in FIGS. 3and 4, the auxiliary grooves 31 each have an opening end portion atwhich each of the auxiliary grooves 31 opens to each of the second maingrooves 12, and a terminating end portion, i.e., a terminating endportion S3, at which each of the auxiliary grooves 31 terminates in eachof the second land portions 22. The auxiliary grooves 31 each formedwith a first groove portion 31A that extends from the opening endportion, i.e., an opening end portion 51, at which each of the auxiliarygrooves 31 opens to each of the second main grooves 12, to a bend pointP, and a second groove portion 31B that extends from the bend point P tothe terminating end portion S3. Positions of the opening end portion 51,the bend point P, and the terminating end portion S3 are determinedbased on a center line that joins centers, in a groove width direction,of the first groove portion 31A and the second groove portion 31B. Inother words, the bend point P represents an intersection point between acenter line 31AA of the first groove portion 31A and a center line 31BBof the second groove portion 31B. The auxiliary grooves 31 are eachshaped by bending the second groove portion 31B at the bend point Ptoward the opening end portion 51 to each of the second main grooves 12so that the terminating end portion S3 lies adjacent to each of thesecond main grooves 12.

It is preferable that the opening end portion 51 of each of theauxiliary grooves 31, which represents an opening portion to each of thesecond main grooves 12, join each of the second main grooves 12. Byallowing the opening end portion of each of the auxiliary grooves 31 toopen outward to each of the second main grooves 12 in the tire lateraldirection, snow performance improves. The first groove portion 31Aaccording to the present embodiment has the opening end portion 51formed adjacent to each of the second main grooves 12. However, theopening end portion S1 may be provided adjacent to each of the firstmain grooves 11.

The groove width represents the maximum distance between the left andright groove walls at the groove opening portion, and is measured whenthe tire is mounted on a specified rim, inflated to the specifiedinternal pressure, and in an unloaded state. In configurations in whichthe land portions include notch portions or chamfered portions on theedge portions thereof, the groove width is measured with reference tothe intersection points where the tread contact surface and extensionlines of the groove walls meet, when viewed in a cross-section normal tothe groove length direction. Additionally, in configuration in which thegrooves extend in a zigzag-like or wave-like manner in the tirecircumferential direction, the groove width is measured with referenceto the center line of the amplitude of the groove walls.

The groove depth represents the maximum distance from the tread contactsurface to the groove bottom, and is measured when the tire is mountedon a specified rim, inflated to the specified internal pressure, and inan unloaded state. Additionally, in configurations in which the groovesinclude an uneven portion or sipes on the groove bottom, the groovedepth is measured excluding these portions.

“Specified rim” refers to an “applicable rim” defined by the JapanAutomobile Tyre Manufacturers Association Inc. (JATMA), a “Design Rim”defined by the Tire and Rim Association, Inc. (TRA), or a “MeasuringRim” defined by the European Tyre and Rim Technical Organisation(ETRTO). Additionally, “specified internal pressure” refers to a“maximum air pressure” defined by JATMA, to the maximum value in “TIRELOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, and to“INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load”refers to a “maximum load capacity” defined by JATMA, the maximum valuein “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined byTRA, and a “LOAD CAPACITY” defined by ETRTO. However, in the case ofJATMA, for a passenger vehicle tire, the specified internal pressure isan air pressure of 180 kPa, and the specified load is 88% of the maximumload capacity.

Auxiliary Groove and First Sipe

In the present embodiment, the auxiliary grooves 31 each open to each ofthe second main grooves 12, and each terminate in each of the secondland portions 22. The auxiliary grooves 31 may each open to each of thefirst main grooves 11, instead of the second main grooves 12, and eachterminate in each of the second land portions 22.

The auxiliary grooves 31 are each formed into the shape bending at thebent portion, i.e., the bend point P, and each include the first grooveportion 31A extending from the opening end portion S1 to the bentportion, i.e., the bend point P, and the second groove portion 31Bextending from the bent portion, i.e., the bend point P to theterminating end portion S3. A groove width of the first groove portion31A gradually reduces from the opening end portion S1 to the bend pointP. By providing the auxiliary grooves 31 that each open to each of thefirst main grooves 11 or each of the second main grooves 12, and thateach having the bent portion, i.e., the bend point P, pattern noise andair column resonance are suppressed. With the shape having the bendpoint P presenting edge effects, and the feature in which a groove widthreduces from the opening end portion S1 to the bend point P, allowingsnow inside the auxiliary grooves 31 to easily remove, snow performanceimproves.

The tread portion 1 includes first sipes 41A that are inclined in adirection identical to the direction of the auxiliary grooves 31, andthat cross each of the second land portions 22. The tread portion 1further includes second sipes 41B each having an end that opens to eachof the second main grooves 12, and another end that opens to each of theauxiliary grooves 31. The tread portion 1 still further includes thirdsipes 41C each having an end that opens to each of the first maingrooves 11, and another end that terminates in each of the second landportions 22. The third sipes 41C may each have an end that opens to eachof the first main grooves 11, and another end that opens to each of theauxiliary grooves 31. With the second groove portions 31B each benttoward the opening end portion S1 of each of the first groove portions31A, as well as with the first sipes 41A inclined in the directionidentical to the direction of the auxiliary grooves 31, a residual CFincreases. The first sipes 41A, the second sipes 41B, and the thirdsipes 41C may each be either of a two-dimensional sipe (i.e., flat sipe)and a three-dimensional sipe (i.e., 3D sipe).

The two-dimensional sipe has sipe wall surfaces each formed into astraight shape, when viewed in a cross-section normal to a sipe lengthdirection (viewed in a cross-section including a sipe width directionand a sipe depth direction). The two-dimensional sipe formed into astraight shape is enough, when viewed in a cross-section, as describedabove. The two-dimensional sipe can be formed into a straight shape, azigzag shape, a wave-like shape, or an arc shape, for example, to extendin the sipe length direction.

The three-dimensional sipe has sipe wall surfaces each formed into abent shape to wave in the sipe width direction, when viewed in across-section normal to the sipe length direction, as well as whenviewed in a cross-section normal to the sipe depth direction. Comparedwith the two-dimensional sipe, the three-dimensional sipe presents agreater meshing force between the opposing sipe wall faces and thereforeacts to reinforce the rigidity of each of the land portions. Thethree-dimensional sipe having a structure as described above with thesipe wall surfaces is enough. On a tread contact surface, thethree-dimensional sipes can each be formed into a straight shape, azigzag shape, a wave-like shape, or an arc shape, for example.

Shapes of First and Second Main Grooves

As illustrated in FIGS. 2 and 3, it is preferable that the pair of firstmain grooves 11 and 11 each have groove walls each having short portions11S and long portions 11L to form a zigzag shape, when viewed in a plan.The zigzag shape formed by the groove walls of each of the first maingrooves 11 is formed by alternately and repeatedly disposing the longportions 11L and the short portions 11S in the tire circumferentialdirection. It is preferable that a length of each of the long portions11L in the tire circumferential direction range from 10 times or more to25 times or less of a length of each of the short portions 11S in thetire circumferential direction, for example.

As illustrated in FIGS. 2 and 3, it is preferable that the pair ofsecond main grooves 12 and 12 each have groove walls each having longportions 12L and short portions 12S to form a zigzag shape, when viewedin a plan. The zigzag shape formed by the groove walls of each of thesecond main grooves 12 is formed by alternately and repeatedly disposingthe long portions 12L and the short portions 12S in the tirecircumferential direction. It is preferable that a length of each of thelong portions 12L in the tire circumferential direction range from 10times or more to 25 times or less of a length of each of the shortportions 12S in the tire circumferential direction, for example.

On the groove walls, which lie outside in the tire lateral direction,and the groove walls, which lie inside in the tire lateral direction andadjacent to the tire equatorial plane CL, of the pair of first maingrooves 11 and 11, the long portions 11L and the short portions 11S aredisposed at identical pitches. However, arrangement phases of the longportions 11L and the short portions 11S differ between each of thegroove walls, which lie outside in the tire lateral direction, and eachof the groove walls, which lie inside in the tire lateral direction andadjacent to the tire equatorial plane CL. Distances d11 are created dueto this phase shifting as a result.

On the groove walls, which lie outside in the tire lateral direction,and the groove walls, which lie inside in the tire lateral direction andadjacent to the tire equatorial plane CL, of the pair of second maingrooves 12 and 12, the long portions 12L and the short portions 12S aredisposed at identical pitches. However, arrangement phases of the longportions 12L and the short portions 12S differ between each of thegroove walls, which lie outside in the tire lateral direction, and eachof the groove walls, which lie inside in the tire lateral direction andadjacent to the tire equatorial plane CL. Distances d12 are created dueto this phase shifting as a result.

It is preferable that inclination directions of the zigzag shapes of thefirst main grooves 11 and the second main grooves 12 be identical to thedirection of the auxiliary grooves 31. Note that, when inclinationdirections are identical, inclination directions in the tire lateraldirection with respect to the tire circumferential direction isidentical. With the first main grooves 11 and the second main grooves 12each formed into the zigzag shape as described above, air columnresonance is suppressed, as well as edge effects improve snowperformance. With the first main grooves 11 and the second main grooves12 both inclined in the direction identical to the direction of theauxiliary grooves 31, a residual CF increases.

Circumferential Narrow Groove

On the tread portion 1, the second main grooves 12 and 12 define thethird land portions 23 and 23 outside, in the tire lateral direction, ofthe second main grooves 12. It is preferable that the tread portion 1include circumferential narrow grooves 53 that are provided on the thirdland portions 23, and that extend in the tire circumferential direction.A groove width of each of the circumferential narrow grooves 53 is notparticularly limited, and may be set so as to fall within a range from 1mm to 25 mm inclusive, for example. It is preferable that thecircumferential narrow grooves 53 be each formed into a zigzag shapeinclined in a direction identical to an inclination direction of theauxiliary grooves 31. By providing the circumferential narrow grooves53, pattern noise can be suppressed.

Lug Groove

It is preferable that the tread portion 1 include lug grooves 33 thatare provided on the third land portions 23, and that are notcommunicated with the second main grooves 12. By providing the luggrooves 33, snow performance improves. Due to its non-through style, aircolumn resonance is suppressed.

The lug grooves 33 are inclined in a direction identical to theinclination direction of the auxiliary grooves 31 in regions closer tothe tire equatorial plane CL than the regions X. The regions X refer toregions ranging from 90% or more to 110% or less of a ground contactwidth representing a distance between the ground contact edges Tcentered around the tire equatorial plane CL. When a distance from thetire equatorial plane CL to one of the ground contact edges T isspecified to a value of 50% of the ground contact width, one of theregions X is represented by a region ranging from 50%+/−5% of the groundcontact width.

A straight line 33AA joining a midpoint P33 and a midpoint P34 of thegroove width of each of the lug grooves 33, at both end portions of eachof the regions X is approximately parallel to the tire lateraldirection. The term “approximately parallel” used herein denotes that anangle formed with the straight line 33AA and a straight line along thetire lateral direction is equal to or below a predetermined angle. It ispreferable that an angle α formed with the straight line along the tirelateral direction and the straight line 33AA joining the midpoints,i.e., the midpoint P33 and the midpoint P34, fall within a range of+/−10 degrees or less relative to the tire lateral direction, forexample. In other words, it is preferable that the midpoint P34 lie,around the midpoint P33, at an angle of 10 degrees or less in acounter-clockwise direction (i.e., +10 degrees or less), or at an angleof 10 degrees or less in a clockwise direction (i.e., −10 degrees orless), relative to the straight line parallel to the tire lateraldirection. With the lug grooves 33 configured as described above, aresidual CF can be increased without increasing pattern noise.

Relationship Between Lug Grooves and Second Main Grooves

In FIG. 3, it is preferable that, on the tread portion 1, arrangementpitches, in the tire circumferential direction, of the short portions12S and the long portions 12L on the groove walls, which lie outside inthe tire lateral direction, of the second main grooves 12 be identicalto arrangement pitches in the tire circumferential direction of the luggrooves 33. It is also preferable that end portions T33 of the luggrooves 33 be disposed so as to respectively face the short portions 12Son the groove walls, which lie outside in the tire lateral direction, ofthe second main grooves 12.

In FIG. 3, it is preferable that, on the tread portion 1, each ofdistances d33 between each of boundary portions S2 between each of theshort portions 12S and each of the long portions 12L on each of thegroove walls, which lie outside in the tire lateral direction, of thesecond main grooves 12 and each of the end portions T33, which face thetire equatorial plane CL, of the lug grooves 33 range from 1.0 times ormore to 4.0 times or less of a length of each of the short portions 12Sin the tire circumferential direction. A distance below 1.0 times is notpreferable because a groove area increases, lowering rigidity. Adistance above 4.0 times is not preferable because the inclinationdirection of the lug grooves 33 and the inclination direction of thesecond main grooves 12 would be less likely to match each other. As aresult, a residual CF would be less likely to increase.

The boundary portions S2 each lie within an angular range of +1-04 in adirection from the midpoint P34 of the groove width of each of the luggrooves 33 at one of the end portions, which lies adjacent to the tireequatorial plane CL, of each of the regions X to each of the endportions T33, which face the tire equatorial plane CL, of the luggrooves 33. It is preferable that the angular range of +1-04 be anangular range of +/−5 degrees, for example. Within the angular range,tread rigidity increases, and a residual CF would be further likely toincrease.

Other Sipes

It is preferable that the tread portion 1 include, on the first landportion 21, a plurality of first land portion sipes 42. The plurality offirst land portion sipes 42 are formed and separated at intervals in thetire circumferential direction. The plurality of first land portionsipes 42 are formed so as to extend in the tire lateral direction. Thefirst land portion sipes 42 each have an end that opens to each of thefirst main grooves 11 and another end that terminates in the first landportion 21. The first land portion sipes 42 are not provided on the tireequatorial plane CL. More specifically, the first land portion sipes 42each terminate in front of the tire equatorial plane CL withoutintersecting the tire equatorial plane CL, as well as each open to eachof the first main grooves 11. A width of each of the first land portionsipes 42 is 1.2 mm or less, for example. By providing the first landportion sipes 42 as described above, snow performance can be improvedwithout increasing pattern noise. The first land portion 21 is notprovided with lug grooves.

It is also preferable that the tread portion 1 include, in regionsadjacent to the tire equatorial plane CL than the regions X, third landportion sipes 43 that are 3D sipes inclined in a direction identical tothe inclination direction of the lug grooves 33. By providing the 3Dsipes inclined in the direction identical to the inclination directionof the lug grooves 33, tread rigidity increases, and a residual CF wouldbe further likely to increase.

Inclination Direction of Grooves

As illustrated in FIG. 3, an arrow Y1 extending in parallel to one ofthe groove walls, which lies adjacent to the tire equatorial plane CL,of each of the first main grooves 11 is inclined in the tire lateraldirection so as to approach the tire equatorial plane CL relative to thetire circumferential direction. An arrow Y2 extending in parallel toanother one of the groove walls, which lies away from the tireequatorial plane CL, of the first main grooves 11 is inclined in thetire lateral direction so as to approach the tire equatorial plane CLrelative to the tire circumferential direction.

As illustrated in FIG. 3, an arrow Y3 extending in parallel to one ofthe groove walls, which lies adjacent to the tire equatorial plane CL,of the second main grooves 12 is inclined in the tire lateral directionso as to approach the tire equatorial plane CL relative to the tirecircumferential direction. An arrow Y4 extending in parallel to anotherone of the groove walls, which lies away from the tire equatorial planeCL, of the second main grooves 12 is inclined in the tire lateraldirection so as to approach the tire equatorial plane CL relative to thetire circumferential direction.

As illustrated in FIG. 3, an arrow Y5 extending along a center linepassing through a center of a groove width of each of thecircumferential narrow grooves 53 is inclined in the tire lateraldirection so as to approach the tire equatorial plane CL relative to thetire circumferential direction. As described above, the arrow Y1 to thearrow Y5 are all inclined in the tire lateral direction so as toapproach the tire equatorial plane CL relative to the tirecircumferential direction. A straight line 33BB extending from each ofthe midpoints P34 to each of the end portions T33 is inclined in thetire lateral direction so as to approach the tire equatorial plane CLrelative to the tire circumferential direction. As described above, onthe tread portion 1, the inclination direction of the lug grooves 33 andthe inclination directions of other grooves, i.e., the first maingrooves 11, the second main grooves 12, and the circumferential narrowgrooves 53 are identical. Inclination components of a whole pattern onthe tread portion 1 thus increase. As a result, a residual CF can beincreased.

As illustrated in FIG. 4, a straight line 311 joining the opening endportion S1 and the terminating end portion S3 of each of the auxiliarygrooves 31 is inclined in the tire lateral direction so as to approachthe tire equatorial plane CL relative to the tire circumferentialdirection. On the tread portion 1, the inclination direction of each ofthe auxiliary grooves 31 and the inclination directions of othergrooves, i.e., the first main grooves 11, the second main grooves 12,and the circumferential narrow grooves 53 are identical. In other words,the inclination directions in the tire lateral direction relative to thetire circumferential direction are identical. The inclination componentsof the whole pattern on the tread portion 1 increase. As a result, aresidual CF can be increased.

As illustrated in FIG. 3, the first land portion sipes 42 provided onthe first land portion 21 are inclined in the tire lateral direction soas to approach the tire equatorial plane CL relative to the tirecircumferential direction. The third land portion sipes 43 provided onthe third land portions 23 are inclined in the tire lateral direction soas to approach the tire equatorial plane CL relative to the tirecircumferential direction. Further, as illustrated in FIG. 4, the firstsipes 41A, the second sipes 41B, and the third sipes 41C provided on thesecond land portions 22 are inclined in the tire lateral direction so asto approach the tire equatorial plane CL relative to the tirecircumferential direction. As described above, on the tread portion 1,the inclination directions of the first sipes 41A, the second sipes 41B,the third sipes 41C, the first land portion sipes 42, and the third landportion sipes 43 and the inclination directions of the lug grooves 33and the auxiliary grooves 31 are also identical. In other words, theinclination directions in the tire lateral direction relative to thetire circumferential direction are identical. The inclination componentsof the whole pattern on the tread portion 1 further increase. As aresult, a residual CF can be further increased.

An angle formed with the tire circumferential direction and an arrow Y6extending in parallel to a center line 41AA passing through a center ofa groove width of each of the first sipes 41A is designated to θ1. Anangle formed with the tire circumferential direction and an arrow Y7extending in parallel to a center line 41BB passing through a center ofa groove width of each of the second sipes 41B is designated to θ2. Anangle formed with the tire circumferential direction and an arrow Y8extending in parallel to a center line 41CC passing through a center ofa groove width of each of the third sipes 41C is designated to θ3. Forexample, θ1, θ2, and θ3 are angles each ranging from 40 degrees or moreto 80 degrees or less. In this example, an equation of θ1=θ2=θ3 issatisfied. At least one of θ1, θ2, and θ3 may be another angle.

Relationship with Ground Contact Shape

FIG. 8 is a view illustrating an example of a ground contact shape withrespect to the tread pattern in FIG. 2. In FIG. 8, a ground contactshape GC shows an approximately elliptical shape. On the ground contactshape GC, end portions in the tire lateral direction conform to theground contact edges T.

FIG. 9 is a partial enlarged view of one of the third land portions 23in FIG. 8. In FIG. 9, a tangent line with respect to the ground contactshape GC, which passes through an intersection point P35 between theground contact shape GC and one of the end portions, which lies adjacentto the tire equatorial plane CL, of one of the regions X is designatedto a tangent line S35. It is desirable that an angle θ5 formed with thestraight line 33AA and the tangent line S35 range from 45 degrees ormore to 90 degrees or less. If the angle is below 45 degrees, greatercontact noise would occur between the pneumatic tire 10 and a roadsurface when the end portions of the lug grooves 33 ground, sacrificingquietness.

As described above with reference to FIG. 3, on the regions X, when theangle α formed with the straight line along the tire lateral directionand the straight line 33AA joining the midpoint P33 and the midpoint P34falls within a range of +/−10 degrees or less relative to the tirelateral direction, the angle θ5 can be kept in a range from 45 degreesor more to 90 degrees or less.

Groove Width of Auxiliary Groove

In FIG. 3, it is preferable that a groove width at the bend point Prepresenting the bent portion of the first groove portions 31A of eachof the auxiliary grooves 31 range from 50% or more to 90% or less of agroove width at the opening end portion S1. With a groove width fallingwithin the above described range, snow accumulated in the first grooveportions 31A easily comes off, improving snow performance.

Groove Depth of Auxiliary Groove

Next, a groove depth of the auxiliary grooves 31 will now be described.FIG. 5 is a partial-cut perspective view illustrating one of the secondland portions 22 on the tread portion 1 in FIG. 3. FIG. 6 is across-sectional view of the one of the second land portions 22, takenalong a center of a groove width of one of the first groove portions 31Aon the tread portion 1 in FIG. 3. FIG. 7 is a cross-sectional view ofthe one of the second land portions 22, taken along a center of a groovewidth of one of the second groove portions 31B on the tread portion 1 inFIG. 3. In FIG. 5, the first sipes 41A, the second sipes 41B, and thethird sipes 41C are omitted.

As illustrated in FIGS. 5 and 6, it is preferable that the groove depthof the first groove portion 31A of each of the auxiliary grooves 31gradually increase from the bent portion, i.e., the bend point P, to theopening end portion S1. In other words, it is preferable that the groovedepth gradually change from a groove depth H1 at the bent portion, i.e.,the bend point P, to a groove depth H2 at the opening end portion S1.With the groove depth gradually increasing from the bent portion, i.e.,the bend point P, to the opening end portion S1, snow accumulated in thefirst groove portions 31A easily comes off, improving snow performance.It is preferable that the groove depth H2 at the opening end portion S1of the first groove portion 31A of each of the auxiliary grooves 31range from 110% or more to 150% or less of the groove depth H1 at thebent portion, i.e., the bend point P. With a groove depth falling withinthe above described range, snow accumulated in the first groove portions31A easily comes off, improving snow performance.

As illustrated in FIGS. 5 and 7, it is preferable that a groove depth atthe second groove portion 31B of each of the auxiliary grooves 31 alsogradually increase from the bend point P to the terminating end portionS3. In other words, it is preferable that the groove depth graduallychange from the groove depth H1 at the bent portion, i.e., the bendpoint P, to the groove depth H3 at the terminating end portion S3. Withthe groove depth changing within the above described range, snowaccumulated in the second groove portions 31B easily comes off,improving snow performance.

Examples

Table 1 and Table 2 show the results of performance tests on thepneumatic tire according to the embodiment of the technology. In theperformance tests, a plurality of mutually different pneumatic tireswere also evaluated for residual CF, quietness, and snow performance. Inthe performance tests, the pneumatic tires with a tire size of 205/60R1692H were mounted on rims with a rim size of 16×6.5 J and inflated to anair pressure of 240 kPa. Additionally, a front engine-front drive (FF)passenger car equipped with an engine having a displacement of 1500 ccwas used as a test vehicle.

In the evaluations for residual CF, the pneumatic tires were eachrotated on a flap belt machine. For example, each of the tires wasallowed to pressure contact with a belt face of the flap belt machine. Acornering force was measured as a residual CF when self-aligning torquethat occurred as the tire rotated became 0. The self-aligning torquedenotes a moment that occurs, in a direction orthogonal to a directionof a road surface, about an axis line passing through a center of a tirewhen a slip angle is applied to the rotating tire. A cornering forcedenotes a force that occurs in a direction of the axis line that passesthrough the center of the tire, and that is orthogonal to a directiontoward which the rotating tire advances. The results of the evaluationsfor residual CF were expressed as index values based on the tiresaccording to the conventional examples (i.e., based on a value of 100).In the evaluations, the larger the values, the more preferable theresults.

In the evaluations for quietness, the test vehicle ran on dry roadsurfaces of a test course, and cabin noise was sensory evaluated. Theresults of the evaluations for quietness were expressed as index valuesbased on the tires according to the conventional examples (i.e., basedon a value of 100). In the evaluations, the larger the values, the morepreferable the results.

In the evaluations for snow performance, the test vehicle ran on snowyroad surfaces of a test course, and expert test drivers sensoryevaluated braking performance and driving performance. The results ofthe evaluations for snow performance were expressed as index valuesbased on the tires according to the conventional examples (i.e., basedon a value of 100). In the evaluations, the larger the values, the morepreferable the results.

The pneumatic tires according to Example 1 to Example 16 each included:a pair of first main grooves that were formed on both outer sides, in atire lateral direction, of a first land portion including a tireequatorial plane, and that each extended in a tire circumferentialdirection; a pair of second main grooves that lied outside, in the tirelateral direction, of the above described first main grooves, and thateach extended in the tire circumferential direction; auxiliary groovesthat were formed on each of second land portions between each of theabove described first main grooves and each of the above describedsecond main grooves, that were each open to each of the above describedsecond main grooves, and that each terminated in each of the abovedescribed second land portions; and first sipes that were inclined in adirection identical to a direction of the above described auxiliarygrooves, and that crossed each of the above described second landportions. The above described auxiliary grooves were each formed into ashape bending at a bend point, and each included a first groove portionextending from an opening end portion at which each of the abovedescribed auxiliary grooves opened to the above described bend point,and a second groove portion extending from the above described bendpoint to a terminating end portion at which each of the auxiliarygrooves terminated. A groove width of each of the above described firstgroove portions gradually reduced from the opening end portion to theabove described bend point.

Example 1 to Example 16 were set in accordance with Table 1 and Table 2.In other words, the pneumatic tires were prepared as described below:the first main grooves and the second main grooves were each formed intoa straight shape and a zigzag shape, respectively; the inclinationdirections of the first main grooves and the second main grooves weremade identical to the direction of the auxiliary grooves; the auxiliarygrooves were each formed into a bent shape; the inclination directionsof the first to third sipes were made identical to the direction of theauxiliary grooves; the groove widths at the opening end portions of thefirst groove portions were specified to 5.5 mm and 6 mm, respectively;the groove widths at the bend points of the first groove portions werespecified to 3 mm and 5 mm, respectively; the groove depths at theopening end portions of the first groove portions were specified to 5.5mm and 6 mm, respectively; the groove depths at the bend points of thefirst groove portions were specified to 4 mm, 5 mm, and 6 mm,respectively; the angles of the lug grooves in the regions X relative tothe tire lateral direction were specified to −10 degrees, −5 degrees, 0degrees, +5 degrees, and +10 degrees, respectively; the lug grooves wereinclined and not inclined relative to the tire lateral direction in theregions closer to the tire equatorial plane CL than the regions X,respectively; the circumferential narrow grooves each formed into azigzag shape inclined in the direction identical to the inclinationdirection of the auxiliary grooves were provided and not provided,respectively; the first land portion was provided with the sipes and notprovided with the sipes, respectively; the sipes on the third landportions were each formed into a straight shape (flat shape) and athree-dimensional shape (3D shape), respectively; the ratios between thelength of each of the short portions of each of the second main groovesin the tire circumferential direction and the distance between each ofthe lug grooves and each of the boundaries of each of the second maingrooves were specified to 1.0, 2.0, 3.0, and 4.0, respectively; and thepositional relationships between the inclination of each of the luggrooves and each of the boundary portions of each of the second maingrooves were specified so as to fall within and outside of an angularrange of +/−04, respectively. The ratios between the groove width at theopening end portion of each of the first groove portions and the groovewidth at each of the bend points were 0.5 and 0.9, respectively. Theratios between the groove depth at the bend point of each of the firstgroove portions and the groove depth at each of the opening end portionswere 1.0, 1.1, and 1.5, respectively.

On each of the pneumatic tires according to the conventional examples,each of the main grooves was formed into a straight shape, and each ofthe auxiliary grooves did not bend, but crossed from each of the secondmain grooves to each of the first main grooves. For purpose ofcomparison, some pneumatic tires according to some comparative exampleswere further prepared: in Comparative example 1, main grooves were eachformed into a straight shape; in Comparative example 2, main grooveswere each formed into a zigzag shape, an inclination direction of eachof the main grooves was opposite to a direction of auxiliary grooves,and inclination directions of first to third sipes were opposite to thedirection of the auxiliary grooves.

The pneumatic tires were evaluated for residual CF, quietness, and snowperformance with the evaluation methods described above. The results areshown in Table 1 and Table 2.

As illustrated in Table 1 and Table 2, fine results were acquired forresidual CF, quietness, and snow performance in conditions describedbelow: the first main grooves and the second main grooves were eachformed into a zigzag shape; the inclination directions of the first maingrooves and the second main grooves were identical to the direction ofthe auxiliary grooves, as well as the inclination directions of thefirst to third sipes were identical to the direction of the auxiliarygrooves; the groove width at the bend point of each of the first grooveportions ranged from 50% or more to 90% or less of the groove width atthe opening end portion; the groove depth at the opening end portion ofeach of the first groove portions ranged from 110% or more to 150% orless of the groove depth at the bend point; the angle α formed with thestraight line along the tire lateral direction and the straight linejoining the midpoints of the groove width of each of the lug grooves, atboth the end portions of each of the regions X, fell within a range of+/−10 degrees or less, as well as the inclination direction of the luggrooves in the regions adjacent to the tire equatorial plane CL than theregions X was identical to the direction of the auxiliary grooves; thecircumferential narrow grooves each formed into a zigzag shape inclinedin the direction identical to the inclination direction of the auxiliarygrooves were provided; the first land portion sipes were provided; thethird land portion sipes were each formed into a 3D shape; and thedistance between the boundary portion between each of the short portionsand each of the long portions on one of the groove walls of each of thesecond main grooves and the end portion, which lied adjacent to the tireequatorial plane, of each of the lug grooves ranged from 1.0 times ormore to 4.0 times or less of the length of each of the short portions inthe tire circumferential direction, as well as the boundary portion liedwithin a range of +/−5 degrees of the direction from the midpoint of thegroove width of one of the lug grooves, at the end portion, which liedadjacent to the tire equatorial plane CL, of each of the regions X, tothe end portion, which lied adjacent to the tire equatorial plane CL, ofeach of the lug grooves.

TABLE 1 Conventional Comparative Comparative Example example example 1example 2 1 Shape of main groove Straight Straight Zigzag StraightInclination direction of main groove — — Opposite — direction Shape ofauxiliary groove Crossing Bent shape Bent shape Bent shape Inclinationdirection of sipe — — Opposite Identical direction direction Groovewidth at opening end portion 6 3 6 6 of first groove portion [mm] Groovewidth at bend point of first 6 6 3 3 groove portion [mm] Groove width atbend point/groove 1.0 2.0 0.5 0.5 width at opening end portion Groovedepth at opening end portion 6 6 6 6 of first groove portion [mm] Groovedepth at bend point of first 6 6 6 6 groove portion [mm] Groove depth atopening end 1.0 1.0 1.0 1.0 portion/groove depth at bend point Angle oflug groove on third land 0 0 0 0 portion in region X [deg]Presence/absence of inclination of lug No No No No groove on third landportion in other than region X Presence/absence of circumferential No NoNo No narrow groove Presence/absence of first land portion No No No Nosipe Shape of third land portion sipe Straight Straight StraightStraight Distance between lug groove and — — 0.5 — second maingroove/length of short portion Positional relationship between Outsideof Outside of Outside of Within inclination of lug groove and secondrange range range range main groove Residual CF 100 100 100 103Quietness 100 105 105 105 Snow performance 100 102 105 105 ExampleExample Example Example Example 2 3 4 5 6 Shape of main groove ZigzagZigzag Zigzag Zigzag Zigzag Inclination direction of main grooveIdentical Identical Identical Identical Identical direction directiondirection direction direction Shape of auxiliary groove Bent Bent BentBent Bent shape shape shape shape shape Inclination direction of sipeIdentical Identical Identical Identical Identical direction directiondirection direction direction Groove width at opening end portion 6 6 65.5 6 of first groove portion [mm] Groove width at bend point of first 33 3 5 3 groove portion [mm] Groove width at bend point/groove 0.5 0.50.5 0.9 0.5 width at opening end portion Groove depth at opening endportion 6 6 6 6 5.5 of first groove portion [mm] Groove depth at bendpoint of first 6 4 4 4 5 groove portion [mm] Groove depth at opening end1.0 1.5 1.5 1.5 1.1 portion/groove depth at bend point Angle of luggroove on third land 0 0 0 0 0 portion in region X [deg]Presence/absence of inclination of lug No No No No No groove on thirdland portion in other than region X Presence/absence of circumferentialNo No No No No narrow groove Presence/absence of first land portion NoNo Yes Yes Yes sipe Shape of third land portion sipe Straight StraightStraight Straight Straight Distance between lug groove and 1.0 1.0 2.02.0 2.0 second main groove/length of short portion Positionalrelationship between Within Within Within Within Within inclination oflug groove and second range range range range range main groove ResidualCF 105 105 107 107 107 Quietness 105 107 108 108 108 Snow performance105 107 108 106 106

TABLE 2 Example Example Example Example Example 7 8 9 10 11 Shape ofmain groove Zigzag Zigzag Zigzag Zigzag Zigzag Inclination directionIdentical Identical Identical Identical Identical of main groovedirection direction direction direction direction Shape of auxiliaryBent Bent Bent Bent Bent groove shape shape shape shape shapeInclination direction Identical Identical Identical Identical Identicalof sipe direction direction direction direction direction Groove widthat 6 6 6 6 6 opening end portion of first groove portion [mm] Groovewidth at 3 3 3 3 3 bend point of first groove portion [mm] Groove widthat 0.5 0.5 0.5 0.5 0.5 bend point/groove width at opening end portionGroove depth at 6 6 6 6 6 opening end portion of first groove portion[mm] Groove depth at 4 4 4 4 4 bend point of first groove portion [mm]Groove depth 1.5 1.5 1.5 1.5 1.5 at opening end portion/groove depth atbend point Angle of lug +5 +10 −5 −10 0 groove on third land portion inregion X [deg] Presence/absence No No No No Yes of inclination of luggroove on third land portion in other than region X Presence/absence NoNo No No No of circumferential narrow groove Presence/absence Yes YesYes Yes Yes of first land portion sipe Shape of third land StraightStraight Straight Straight Straight portion sipe Distance between 2.02.0 2.0 2.0 2.0 lug groove and second main groove/length of shortportion Positional Within Within Within Within Within relationshipbetween range range range range range inclination of lug groove andsecond main groove Residual CF 107 108 107 106 110 Quietness 106 103 106103 107 Snow performance 109 110 109 110 109 Example Example ExampleExample Example 12 13 14 15 16 Shape of main groove Zigzag Zigzag ZigzagZigzag Zigzag Inclination direction Identical Identical IdenticalIdentical Identical of main groove direction direction directiondirection direction Shape of auxiliary Bent Bent Bent Bent Bent grooveshape shape shape shape shape Inclination direction Identical IdenticalIdentical Identical Identical of sipe direction direction directiondirection direction Groove width at 6 6 6 6 6 opening end portion offirst groove portion [mm] Groove width at 3 3 3 3 3 bend point of firstgroove portion [mm] Groove width at 0.5 0.5 0.5 0.5 0.5 bendpoint/groove width at opening end portion Groove depth at 6 6 6 6 6opening end portion of first groove portion [mm] Groove depth at 4 4 4 44 bend point of first groove portion [mm] Groove depth 1.5 1.5 1.5 1.51.5 at opening end portion/groove depth at bend point Angle of lug 0 0 00 0 groove on third land portion in region X [deg] Presence/absence YesYes Yes Yes Yes of inclination of lug groove on third land portion inother than region X Presence/absence No No No Yes Yes of circumferentialnarrow groove Presence/absence of Yes Yes Yes Yes Yes first land portionsipe Shape of third Straight Straight Straight Straight 3D land portionsipe Distance between 3.0 4.0 3.0 4.0 3.0 lug groove and second maingroove/length of short portion Positional Within Within Outside WithinWithin relationship between range range of range range range inclinationof lug groove and second main groove Residual CF 108 106 107 107 108Quietness 108 109 108 110 109 Snow performance 108 107 108 107 109

1. A pneumatic tire comprising: a pair of first main grooves formed onboth outer sides, in a tire lateral direction, of a first land portionincluding a tire equatorial plane, the pair of first main groovesextending in a tire circumferential direction; a pair of second maingrooves lying outside, in the tire lateral direction, of the first maingrooves, the pair of second main grooves extending in the tirecircumferential direction; auxiliary grooves formed on each of secondland portions between each of the first main grooves and each of thesecond main grooves, the auxiliary grooves each opening to each of thesecond main grooves, the auxiliary grooves each terminating in each ofthe second land portions; and first sipes inclined in a directionidentical to a direction of the auxiliary grooves, the first sipescrossing each of the second land portions, wherein the auxiliary groovesare each formed into a shape bending at a bend point, and each include:a first groove portion extending from an opening end portion at whicheach of the auxiliary grooves opens to the bend point; and a secondgroove portion extending from the bend point to a terminating endportion at which each of the auxiliary grooves terminates, and wherein agroove width of each of the first groove portions gradually reduces fromthe opening end portion to the bend point.
 2. The pneumatic tireaccording to claim 1, wherein the pair of first main grooves and thepair of second main grooves are each formed into a zigzag shape havinggroove walls having short portions and long portions, when viewed in aplan, and wherein an inclination direction of the zigzag shapes isidentical to the direction of the auxiliary grooves.
 3. The pneumatictire according to claim 1, wherein the second main grooves define thirdland portions outside, in the tire lateral direction, of the second maingrooves, and wherein lug grooves are further provided on the third landportions, the lug grooves not communicating with the second maingrooves.
 4. The pneumatic tire according to claim 3, further comprisingcircumferential narrow grooves provided on the third land portions, thecircumferential narrow grooves each extending in the tirecircumferential direction, the circumferential narrow grooves each beingformed into a zigzag shape inclined in a direction identical to aninclination direction of the auxiliary grooves.
 5. The pneumatic tireaccording to claim 3, wherein the lug grooves are inclined, in regions Xranging from 90% or more to 110% or less of a ground contact widthcentered around the tire equatorial plane, at an angle α in a range of+/−10 degrees or less, the angle α being formed with a straight linealong the tire lateral direction and a straight line joining midpoints,at both end portions of each of the regions X, of a groove width of eachof the lug grooves, and wherein, in regions each lying closer to thetire equatorial plane than the regions X, the lug grooves are inclinedin a direction identical to the inclination direction of the auxiliarygrooves.
 6. The pneumatic tire according to claim 3, further comprising,in regions each lying closer to the tire equatorial plane than regions Xranging from 90% or more to 110% or less of a ground contact widthcentered around the tire equatorial plane, three-dimensional (3D) sipesinclined in a direction identical to the inclination direction of thelug grooves.
 7. The pneumatic tire according to claim 3, wherein adistance between a boundary portion between each of short portions andeach of long portions of groove walls of the second main grooves and anend portion, lying adjacent to the tire equatorial plane, of each of thelug grooves ranges from 1.0 times or more to 4.0 times or less of alength of each of the short portions in the tire circumferentialdirection, and wherein the boundary portion lies within a range of +/−5degrees of a direction from one of midpoints of the groove width of eachof the lug grooves, at the end portion of each of regions X ranging from90% or more to 110% or less of a ground contact width centered aroundthe tire equatorial plane, the end portion lying adjacent to the tireequatorial plane, to the end portion, lying adjacent to the tireequatorial plane, of each of the lug grooves.
 8. The pneumatic tireaccording to claim 1, wherein, in each of the first groove portions, agroove depth gradually increases from the bend point to the opening endportion.
 9. The pneumatic tire according to claim 1, wherein, in each ofthe first groove portions, the groove width at the bend point rangesfrom 50% or more to 90% or less of the groove width at the opening endportion.
 10. The pneumatic tire according to claim 1, wherein, in eachof the first groove portions, a groove depth at the opening end portionranges from 110% or more to 150% or less of the groove depth at the bendpoint.
 11. The pneumatic tire according to claim 1, wherein the firstmain grooves are each disposed outside, in the tire lateral direction,of the tire equatorial plane, wherein the first main grooves define thefirst land portion, and wherein first land portion sipes are furtherincluded, the first land portion sipes each opening to each of the firstmain grooves, the first land portion sipes each terminating in the firstland portion.
 12. The pneumatic tire according to claim 1, wherein theauxiliary grooves are inclined in the tire lateral direction so that astraight line joining each of the opening end portions and each of theterminating end portions approaches the tire equatorial plane relativeto the tire circumferential direction.
 13. The pneumatic tire accordingto claim 1, wherein the pair of first main grooves are each formed intoa zigzag shape having groove walls having short portions and longportions, when viewed in a plan, wherein the zigzag shapes are eachformed with the long portions and the short portions alternately andrepeatedly disposed in the tire circumferential direction, and wherein alength of each of the long portions in the tire circumferentialdirection ranges from 10 times or more to 25 times or less of a lengthof each of the short portions in the tire circumferential direction. 14.The pneumatic tire according to claim 13, wherein the pair of first maingrooves are each formed with a groove wall lying outside in the tirelateral direction and a groove wall lying inside in the tire lateraldirection and adjacent to the tire equatorial plane, wherein the longportions and the short portions are disposed at identical pitches, andwherein arrangement phases of the long portions and the short portionsdiffer between each of the groove walls lying outside in the tirelateral direction and each of the groove walls lying inside in the tirelateral direction and adjacent to the tire equatorial plane.
 15. Thepneumatic tire according to claim 1, wherein the pair of second maingrooves are each formed into a zigzag shape having groove walls havingshort portions and long portions, when viewed in a plan, wherein thezigzag shapes are each formed with the long portions and the shortportions alternately and repeatedly disposed in the tire circumferentialdirection, and wherein a length of each of the long portions in the tirecircumferential direction ranges from 10 times or more to 25 times orless of a length of each of the short portions in the tirecircumferential direction.
 16. The pneumatic tire according to claim 15,wherein the pair of second main grooves are each formed with a groovewall lying outside in the tire lateral direction and a groove wall lyinginside in the tire lateral direction and adjacent to the tire equatorialplane, wherein the long portions and the short portions are disposed atidentical pitches, and wherein arrangement phases of the long portionsand the short portions differ between each of the groove walls lyingoutside in the tire lateral direction and each of the groove walls lyinginside in the tire lateral direction and adjacent to the tire equatorialplane.
 17. The pneumatic tire according to claim 15, wherein anarrangement pitch in the tire circumferential direction of each of thelong portions and each of the short portions on each of the pair ofsecond main grooves and an arrangement pitch in the tire circumferentialdirection of lug grooves provided on each of third land portionsrespectively defined outside, in the tire lateral direction, of thesecond main grooves, the lug grooves respectively not communicating withthe second main grooves, are identical to each other, and wherein an endportion of each of the lug grooves is disposed to face each of the shortportions on each of the groove walls lying outside, in the tire lateraldirection, of the second main grooves.